A bearing device is provided for example with a slide member and a housing configured to hold the slide member. The slide member is configured to slide with respect to a counter member such as a shaft member. The rotation of the shaft member causes micro slipping between the slide member and the housing. The micro slipping may cause fretting damages to the slide member and/or the housing.
Thus, in a conventional bearing device disclosed for example in JP 2002-174244 A, a hard coating having a hardness greater than 1000 HV is applied over the outer peripheral surface of the slide member configured to contact the housing or the inner peripheral surface of the housing configured to contact the slide member. The hard coating applied to the slide member or the housing increases the hardness of the contact surface and reduces fretting wears.
However, bearing devices are required to fulfill further challenging requirements imposed by improved engine performance. Because an increase in the amount of relative sliding and in the amount of deformation even in minute regions of the outer peripheral surface of the slide member and the inner peripheral surface of the housing affect the performance of the bearing device, high fretting resistance is one of the key performance factors of the bearing device. In JP 2002-174244 A, the protective hard coating may not be able to adapt to the increase in the amount of relative sliding and deformation and may eventually breakdown. The breakdown of the hard coating may cause the outer peripheral surface of the slide member and the inner peripheral surface of the housing to become exposed and lead to fretting damages.